WO2004057725A1

WO2004057725A1 - Rotor for an electric motor

Info

Publication number: WO2004057725A1
Application number: PCT/DK2003/000860
Authority: WO
Inventors: Niels Christian Weihrauch
Original assignee: Danfoss Compressors Gmbh
Priority date: 2002-12-19
Filing date: 2003-12-12
Publication date: 2004-07-08
Also published as: AU2003287879A1; DE10261762B4; DE10261762A1

Abstract

The invention relates to a rotor for an electric motor, especially a line-start electric motor, comprising axially extending receiving regions (20 to 25) for conductive rods and axially extending receiving regions (4 to 7) for permanent magnets, which are embodied and arranged in a curved manner. In order to increase the starting torque, the receiving regions (4 to 7) for permanent magnets and/or the permanent magnets themselves have different radii of curvature.

Description

Rotor for an electric motor

The invention relates to a rotor for an electric motor, in particular a line-start electric motor, with receiving spaces for conductor bars that run in the axial direction and with receiving spaces for permanent magnets that run in the axial direction and that are curved and arranged.

Hybrid three-phase motors that represent a combination of a three-phase asynchronous motor with a three-phase synchronous motor are referred to as line-start electric motors. Such a line-start electric motor comprises a stator, which is also referred to as a stator, with a plurality of stator or stator windings. The stator windings generate a rotating field that generates a voltage in a rotor or rotor, which causes the rotor to rotate. The rotor of a line-start electric motor has features of the rotor of a three-phase asynchronous motor as well as features of the rotor of a three-phase synchronous motor. Line start motors can also be designed for single-phase power supplies, possibly with an operating capacitor.

In the rotor of a three-phase asynchronous motor, which is also referred to as an induction motor, conductor bars, for example made of aluminum or copper, are arranged essentially in the axial direction. The conductor bars can be connected by short-circuit rings on the end faces of the rotor. The conductor bars together with the short-circuit rings form the rotor winding and can have the shape of a cage, which is why such a rotor is also referred to as a squirrel-cage rotor. In operation, the rotating field of the stator winding causes a change in the flux in the conductor loops of the rotor, which is initially stationary. The flow rate of change is proportional to the rotating field speed. The induced voltage causes current to flow in the rotor conductor bars connected by the short-circuit rings. The magnetic field generated by the rotor current causes a torque that rotates the rotor in the direction of rotation of the stator rotating field. If the rotor reached the speed of the stator rotating field, the flux change in the conductor loop under consideration would be zero and thus the torque causing the rotation. The rotor speed is therefore always lower than the rotating field speed in three-phase asynchronous motors. The rotor therefore does not run mechanically in synchronism with the rotating field speed. Permanent magnets can be arranged in the rotor of a three-phase synchronous motor, for example, which generate a rotating magnetic field during operation. When the stator winding is supplied with three-phase current, the poles of the rotor are attracted by the opposite poles of the stator rotating field and shortly afterwards repelled by its poles of the same type. Due to its inertia, the rotor cannot immediately follow the stator speed. If, however, the rotor has approximately reached the speed of the stator rotating field, then the rotor is, so to speak, drawn into the stator rotating field speed and continues to run with it. This means that after the rotor starts up, it rotates synchronously with the stator rotating field speed.

The rotor of a line start electric motor includes both permanent magnets and conductor bars. The conductor bars form a starting aid for the rotor. When the speed of the stator rotating field has approximately been reached, the permanent magnets are effective. The line start electric motor thus combines the good starting properties of an asynchronous motor, i.e. the large starting torque, with the high efficiency of the synchronous motor. When the motor starts, the conductor bars develop their effect, whereas the permanent magnets actually only have a disruptive role when the motor starts. In contrast, during synchronous operation, for example at 50 Hz or 3000 rpm, the permanent magnets develop their effect, whereas the conductor bars then no longer contribute to the generation of the torque, since no voltage is induced in the conductor bars in synchronous operation.

The magnetic field existing in the operation of the line-start electric motor in an air gap between the rotor and stator comprises two components. The first component of the resulting field is caused by the stator windings. This is also known as a rotating field. The second component of the resulting field is caused by the permanent magnets, which can also be referred to as permanent magnets. In the operation of conventional line-start electric motors, as are known for example from US 4,403,161, the magnetic field generated by the stator cannot penetrate the rotor unhindered, because the magnetic field generated by the stator cannot pass through the permanent magnets in their main magnetic axis, and In their non-magnetic axis, magnetic flow barriers in the rotor prevent unrestricted flow. This reduces the starting torque. The object of the invention is to provide a rotor according to the preamble of claim 1, with which the starting torque of a conventional line-start electric motor can be increased.

The object is achieved in a rotor for an electric motor, in particular a line-start electric motor, with receiving spaces for conductor bars that run in the axial direction and with receiving spaces for permanent magnets that are curved and arranged in the axial direction, in that the receiving spaces for Permanent magnets and / or the permanent magnets themselves have different radii of curvature. The use of permanent magnets, which do not have a constant radius of curvature, such as in the case of the electric motors known from US Pat. No. 4,403,161, but have different radii of curvature, for example in the form of an ellipse, means that the magnetic field generated by the stator windings can penetrate the rotor better. Starting from the stator windings, a stronger magnetic field can thus be passed through the rotor, which leads to a higher starting or starting torque.

A preferred exemplary embodiment of the rotor is characterized in that a plurality of permanent magnets are arranged in such a way that they generate a permanent magnetic field with a permanent magnet axis and a neutral axis, and in that the receiving spaces for the permanent magnets and / or the

Permanent magnets themselves are so curved and arranged around the axis of rotation of the rotor that the distance between the receiving spaces for the permanent magnets and / or the permanent magnets themselves and the receiving spaces for the conductor bars, viewed in cross section through the rotor, in the region of the permanent magnet axis is larger than in the area of the neutral axis. This creates sufficient space for the field lines of the magnetic field generated by the stator.

Another preferred exemplary embodiment of the rotor is characterized in that the receiving spaces for the permanent magnets and / or the permanent magnets themselves, viewed in cross section through the rotor, have the shape of arcs which are arranged in the form of an ellipse, the main axis of which is aligned with the neutral axis and whose minor axis coincides with the permanent magnet axis. This arrangement has changed in terms of distribution of the magnetic field lines during operation of the device according to the invention has proven to be particularly advantageous.

Another preferred exemplary embodiment of the rotor is characterized in that the receiving spaces for the permanent magnets and / or the permanent magnets themselves, viewed in cross section through the rotor, are less curved in the area of the intersection points with the permanent magnet axis than in the area of the intersection points with the neutral axis. It is thereby achieved that the permanent magnets are not so strongly curved about the axis of rotation of the rotor, but rather extend in the direction of the neutral axis. As a result, the permanent magnetic field generated by the permanent magnets can expand as wide as possible into the air gap between the rotor and stator when the electric motor is in synchronous operation.

Another preferred exemplary embodiment of the rotor is characterized in that the permanent magnetic field generated by the permanent magnets, based on the rotor cross section, extends over an angular range of more than 300 °, in particular over an angular range of approximately 340 °. With these values, the best results were achieved in tests carried out within the scope of the present invention.

Another preferred exemplary embodiment of the rotor is characterized in that the receiving spaces for the conductor bars in at least one

Sector of the rotor have a substantially elongated cross section, and in that the receiving spaces for the conductor bars in this sector, viewed in cross section, are curved along their longitudinal axis. In tests carried out within the scope of the present invention, it has been found that the torque fluctuations in conventional line-start electric motors are due to the fact that the course of the field strength of the resulting magnetic field in the air gap between the stator and rotor is not sinusoidal over the angle of rotation, but, at least partially, is angular. Due to the design and arrangement of the receiving spaces for conductor bars according to the invention, an approximately sinusoidal course can be achieved during operation.

The above task is for an electric motor, especially a line-start electric motor, with a stator that has a large number of windings and has a rotor receiving space with an in particular circular cross section, solved in that a previously described rotor is rotatably received in the rotor receiving space. Due to the approximately sinusoidal course of the magnetic field strength of the permanent magnetic field over the rotor rotation angle, the rotor according to the invention leads to improved starting properties, in particular to better synchronization.

Further advantages, features and details of the invention result from the following description, in which various exemplary embodiments are described in detail with reference to the drawing. Show it:

Figure 1 shows a cross section through a rotor according to a first embodiment of the invention;

FIG. 2 shows a reduced representation of the rotor from FIG. 1 with field lines of the magnetic field generated by the permanent magnets;

3 shows the rotor from FIG. 2 with field lines of the magnetic field generated by a stator;

Figure 4 shows a cross section through a rotor according to another embodiment of the invention and

Figure 5 shows a cross section through a rotor according to another embodiment of the invention.

FIG. 1 shows a rotor 1 of a line start electric motor in cross section. The rotor 1 has a central through hole 2, which serves to receive a shaft (not shown), via which a torque generated by the electric motor can be output.

Around the through hole 2 around four receiving spaces 4, 5, 6 and 7 for permanent magnets 10, 11, 12 and 13 are arranged. The receiving spaces 4 to 7 extend in the axial direction at least over part of the length of the rotor 1. When viewed in cross section, the four receiving spaces 4 to 7 for the permanent magnets 10 to 13 are arranged in the shape of an ellipse. The poles of the permanent magnets 10 to 13 are each designated by the capital letters N for the north pole and S for the south pole. The arrangement of the perma- Magnets 10 to 13 lead to the formation of a magnetic field, the field strength of which is zero along a neutral axis 16 and greatest along a magnetic axis 17. The neutral axis 16 is also referred to as the neutral axis.

To the outside, the rotor 1 is delimited by a circular cylinder surface, on the circumference of which a large number of receiving spaces 20 to 25 and 28, 29 are arranged for conductor bars. The receiving spaces for conductor bars (not shown) extend in the axial direction over the entire length of the rotor 1. The rotor 1 is symmetrical in relation to the neutral axis 16 and the magnetic axis 17. Therefore, for reasons of clarity, only the receiving spaces 20 to 25 and 28, 29 for the conductor bars are provided with reference numerals.

Each receiving space for a conductor bar, which can also be referred to as a receiving space for a conductor winding, comprises two side walls 31 and 32, which are connected by a semicircular connecting wall 34. At the other end, the elongated receiving spaces for the conductor bars are tapered or blunt. The distances 35 to 39 between the outwardly facing ends of the receiving spaces for the conductor bars are constant.

In Figure 1 it can be seen that the two side walls of the receiving space 28 are concave. In contrast, the two side walls of the receiving space 29 are convex. The receiving space 28 is divided into two equal halves by the neutral axis 16 and the receiving space 29 by the magnetic axis 17. The receiving spaces 20 to 25 arranged between the receiving spaces 28 and 29 and thus between the neutral axis 16 and the magnetic axis 17 each have a convex and a concave side wall. The radius of curvature of the receiving spaces 20 to 25 decreases from the neutral axis 16 to the magnetic axis 17. This means that the receiving space 20 has the largest and the receiving space 25 the smallest radii of curvature.

In Figure 2, the magnetic field generated by the permanent magnets 10 to 13 is partially shown in the form of magnetic field lines.

FIG. 3 shows the magnetic field generated by a stator (not shown) during the asynchronous starting of the rotor in the form of magnetic field lines partially shown. The magnetic flux through the rotor 1 is indicated in FIG. 3 by arrows 48 and 49.

The curved receiving spaces for the conductor bars, which can also be referred to as grooves, provide the advantage that the magnetic field generated by the permanent magnets is passed through the rotor 1 in a controlled manner during operation of the line-start electric motor (not shown). As a result, an approximately sinusoidal course of the field strength of the resulting magnetic field can be generated in the air gap between the stator and rotor during operation of the electric motor.

The curvature of the grooves or receiving spaces for the conductor bars has the primary function during the synchronous operation of the electric motor to distribute the magnetic field generated by the permanent magnets sinusoidally in the air gap between the rotor and the stator. As a result, the magnetic field will be weakest in the area of the neutral axis and strongest in the area of the magnetic axis.

In addition, the curved design of the receiving spaces for the conductor bars and the special arrangement of the conductor bars when the electric motor starts up creates a lot of space for the magnetic field of the stator which penetrates the rotor. As can be seen in FIG. 3, there is sufficient space between the receiving spaces 24 and 25 for the conductor bars and the permanent magnet 11 for the passage of the magnetic field lines. This avoids magnetic bottlenecks that could lead to undesired saturation of the rotor plate. The special arrangement of the permanent magnets increases the available space.

It is achieved with the invention that the magnetic field is controlled when the electric motor starts up so that gaps in the magnetic field which are caused by the permanent magnets are filled.

In Figure 4, a rotor receiving space 101 of the stator is shown schematically in cross section by a circle. A rotor 102 is rotatably received in the rotor receiving space 101. The rotor 102 has an elliptical cross section. In the vicinity of the outer circumference of the rotor 102, receiving spaces 104, 105, 106 are arranged distributed uniformly over the circumference of the rotor 102. The receiving spaces 104, 105 and 106 for conductor bars each have one circular cross section. Radially within the receiving spaces 104 to 106 for conductor bars, two receiving spaces 110 and 111 for permanent magnets are arranged. The receiving spaces 110 and 111 for permanent magnets, like the receiving spaces 104 to 106 for conductor bars, extend in the axial direction of the substantially circular-cylindrical rotor 102. The receiving spaces 110 and 111 for permanent magnets are arranged and formed curved around the axis of rotation of the rotor, and with different radii of curvature. The receiving spaces 110 and 111 have the shape of arcs which are arranged in the shape of an ellipse.

In the center, the rotor has a central through hole 117 which serves to receive a shaft which can be connected to the rotor 102 in a rotationally fixed manner. The torque generated by the electric motor can be output via the shaft (not shown).

Permanent magnets 114 and 115, which generate a permanent field, are received in the receiving spaces 110 and 111. The magnetic field generated by the permanent magnets 114 and 115 is indicated in FIG. 4 by magnetic field lines 120, 121. The permanent magnetic field generated by the permanent magnets 114 and 115 has a magnetic axis 122 and a neutral axis 123. The magnetic field strength is greatest along the magnetic axis 122. Along the neutral axis 123, the magnetic field strength of the permanent magnetic field is zero.

The rotor 102 has a greater thickness along the magnetic axis 122 than along the neutral axis 123. Accordingly, the rotor 2 has the shape of an ellipse on its outer circumference, the main axis of which coincides with the magnetic axis 122 and the secondary axis of which coincides with the neutral axis 123. The ellipse formed by the receiving spaces 110 and 111 for the permanent magnets 114 and 115 is arranged perpendicular to the ellipse forming the outer circumference of the rotor 102. The main axis of the ellipse formed by the receiving spaces 110 and 111 coincides with the neutral axis 123. The minor axis of the ellipse formed by the receiving spaces 110 and 111 coincides with the magnetic axis 122.

The use of a rotor which is larger in the direction of the magnetic axis 122 of the permanent magnets 114 and 115 respectively has a greater thickness than in the direction of the neutral axis 123, means that the distance between the rotor 102 and the rotor receiving space 101 of the stator varies, that is to say the air gap formed between the rotor 102 and the rotor receiving space 101 of the stator is variable. The air gap is smallest along the magnetic axis 122 and largest along the neutral axis 123.

In the embodiment shown in FIG. 4, the permanent magnets 114 and 115 do not fill the entire cross section of the receiving spaces 110 and 111. The empty or air-filled parts of the receiving spaces 0 110 and 111 do not generate a magnetic field, which can be seen from the course of the magnetic field lines 120, 121. The distance between the magnetic field lines in the air gap between the rotor 102 and the rotor receiving spaces 101 of the stator is a measure of the electric field strength. It can be seen from FIG. 4 that the magnetic field strength is greatest where the rotor 102 is arranged very close to the rotor receiving space 101 of the stator. To the right and left of the magnetic axis 122, the magnetic field generated by the permanent magnets 114 and 115 becomes weaker, which is desirable. It is thereby achieved that the magnetic field strength in the air gap between the rotor 102 and the rotor receiving space 101 of the stator is approximated to a sinusoidal shape as a function of the angle of rotation of the rotor.

FIG. 5 shows a rotor 102 'in cross section, which is similar to the rotor 102 shown in FIG. 4. However, the receiving spaces 110 'and 111' are completely filled with permanent magnets 114 'and 115'. 5 shows magnetic field lines 150, 151 of the magnetic field generated by the stator windings (not shown) 5. The magnetic axis of the magnetic field generated by the stator windings is designated 154. The magnetic axis 152 of the permanent magnetic field generated by the permanent magnets 114 'and 115' runs perpendicular to this. The radii of curvature of the permanent magnets 114 'and 115' are significantly larger in the region of the intersections with the magnetic axis 152 than at the ends of the permanent magnets. It follows that the distance F between the passage 117 and the permanent magnets 114 ', 115' is significantly larger than the distance G.

The starting torque or starting torque of a line-start electric motor can be increased by the varying radius of curvature of the permanent magnets become. The permanent magnets are preferably oval or in the form of an ellipse. The curved design or arrangement of the permanent magnets has the advantage over an angular or circular arrangement that the magnetic field generated by the stator windings can penetrate the rotor better. 5 shows where the field lines 150, 151 enter the rotor from the stator, run through the rotor and re-enter the stator on the opposite side. As can be seen in FIG. 5, there is enough space between the permanent magnets and the conductor bars or the receiving spaces for the conductor bars for the magnetic field lines of the stator magnetic field. This means that no magnetic bottlenecks are caused, as is the case with conventional line-start electric motors. The permanent magnets can either be formed in one piece, or can be formed from a plurality of magnet segments.

Claims

Expectations

1.Rotor for an electric motor, in particular a line-start electric motor, with receiving spaces (20 to 25; 104 to 106) extending in the axial direction for conductor bars and with receiving spaces (4 to 7; 110, 111) extending in the axial direction for permanent magnets ( 114, 115), which are curved and arranged, characterized in that the receiving spaces (4 to 7; 110, 111) for the permanent magnets and / or the permanent magnets (114, 115) have different radii of curvature.

2. Rotor according to claim 1, characterized in that a plurality of permanent magnets (114, 115) are arranged such that they generate a permanent magnetic field with a permanent magnet axis (17, 122) and a neutral axis (16; 123), and in that the receiving spaces (4 to 7 ; 110,111) for permanent magnets and / or the permanent magnets themselves are so curved and arranged around the axis of rotation of the rotor that the distance between the receiving spaces (4 to 7; 110,111) for permanent magnets and / or the permanent magnets themselves and the receiving spaces (20th to 25; 104 to 106) for conductor bars, viewed in cross section through the rotor, is larger in the area of the magnetic axis (17, 122) than in the area of the neutral axis (16, 123).

3. Rotor according to claim 2, characterized in that the receiving spaces (4 to 7; 110, 11) for the permanent magnets and / or the permanent magnets themselves, viewed in cross section through the rotor, have the shape of arcs which are in the form of an ellipse are arranged, the main axis of which coincides with the neutral axis (16; 123) and the secondary axis of which coincides with the permanent magnet axis (17; 122).

4. Rotor according to claim 2 or 3, characterized in that the receiving spaces (4 to 7; 110, 111) for the permanent magnets and / or permanent magnets themselves, viewed in cross section through the rotor, in the region of the intersection points with the permanent magnet axis (17; 122) are less curved than in the area of the intersection with the neutral axis (16; 123).

5. Rotor according to one of the preceding claims, characterized in that the permanent magnet generated by the permanent magnets Field, based on the rotor cross-section, extends over an angular range of more than 300 °, in particular over an angular range of approximately 340 °.

6. Rotor according to one of the preceding claims, characterized in that the receiving spaces (20 to 25) for conductor bars in at least one sector of the rotor have a substantially elongated cross section, and in that the receiving spaces (20 to 25) for the conductor bars in this sector, viewed in cross section, are curved along its longitudinal axis.

7. Electric motor, in particular line-start electric motor, with a stator which has a plurality of windings and a rotor receiving space with a particularly circular cross section, characterized in that a rotor according to one of the preceding claims is rotatably received in the rotor receiving space.